Process for deoxidizing copper with natural gas-air mixture

ABSTRACT

A process for reducing the oxygen content of molten copper. A mixture of natural gas and air is introduced under the surface of a bath of molten copper, wherein the natural gas reacts with the oxygen in the air to partially oxidize the hydrocarbon constituents of the natural gas to form a reducing gas mixture containing hydrogen and carbon monoxide. The reducing gas mixture reduces the oxygen contained in the copper. In a preferred embodiment, air is introduced over the surface of the bath to react with unreacted material emanating from the surface of the bath, forming a reducing gas mixture over the bath which aids in reducing the oxygen content of the copper and decreases the emission of pollutants into the atmosphere.

United States Patent [72] inventors Russell R. Beck;

Charles W. Anderson; Martin E. Messner, all oi Salt Lake City, Utah [21] AppL No. 821,800 [22] Filed May 5,1969 [45] Patented Nov. 9, 1971 [73] Assignee Kennecott Copper Corporation New York, N.Y.

[54] PROCESS FOR DEOXIDIZING COPPER WITH NATURAL GAS-AIR MIXTURE 8 Claims, 1 Drawing Fig.

[52] U.S. Cl 75/76.

' 7 75/93 [51] int. Cl C22b 9/08, C22b 15/00. C22b 15/14 [50] Field of Search 75/72-76 [56] References Cited UNlTED STATES PATENTS 3,528,802 9/1970 Morris et al. 75/76 3,529,956 9/l970 Foard et al.... 75/76 57,969 9/1866 Reese 266/25 2,989,397 6/l96l Kuzell .a 75/76 OTHER REFERENCES Huttl, John B., Poling" Becomes Ancient History at Phelps Dodge Smelters, in Engineering and Mining Journal, July I96], McGraw-Hill Publishing Co. Inc, pp. 82 85 Primary E.\'umine'r-L. Dewayne Rutledge Axrislanl Examiner-Joseph E. Lcgru Almrne \-.s-John L. Sniado and Mallinckrodt and Mallinckrodt ABSTRACT: A process for reducing the oxygen content of molten copper. A mixture ofnatural gas and air is introduced under the surface of a bath of molten copper, wherein the natural gas reacts with the oxygen in the air to partially oxidize the hydrocarbon constituents of the natural gas to form a reducing gas mixture containing hydrogen and carbon monoxide. The reducing gas mixture reduces the oxygen contained in the copper, in a preferred embodiment. air is introduced over the surface of the bath to react with unreacted material emanating from the surface of the bath. forming a reducing gas mixture over the bath which aids in reducing the oxygen content of the copper and decreases the emission of pollutants into the atmosphere.

PAIENTEDuuv 9l97l 3,619,177

RELATIVELY CLEAN GASEOUS EFFLUENT MRTLQE 955s MOLTEN COPPER D AR BATH AN INVENTORS RUSSELL R. BECK CHARLES W. ANDERSON BY MARTIN E. MESSNER ,[LL I AT TORNE YS PROCESS FOR DEOXIDIZING COPPER WITH NATURAL GAS-AIR MIXTURE BACKGROUND OF THE INVENTION Field: This invention relates to the deoxidation of molten copper in copper refining operation, a procedure which is commonly described as poling."

State of the Art: In the refining of copper obtained from copper smelting operations, it is customary to remove sulfur and other impurities from the molten copper by oxidation. This is normally accomplished by introducing air into a bath of the molten copper to oxidize the impurities. Excess oxygen in the resulting molten copper must be removed to provide a suitable product for casting. It has long been the practice in the copper processing industry to deoxidize such molten copper by introducing green logs or poles into the bath. Hence the term poling is often used to designate processes in general for deoxidizing molten copper.

Numerous attempts have been made to find a substitute for the relatively expensive and dangerous practice of poling the copper with logs. Various proposals have been made for the injection of producer gases into the molten copper to be deoxidized, see for example US. Pat. Nos. 433,086; 746,246; and 900,345. Another proposal has been made to introduce reducing gas into the furnace above the surface of the copper bath, accompanied by the injection of steam within the bath to agitate and expose the molten copper to the reducing atmosphere above the bath, see US. Pat. No. 1,836,196.

Various alkane hydrocarbons and natural gas have been used, but have been found to be inefficient and highly undesirable from the standpoint of carbon emission and related air pollution problems.

Considerable practical success has been achieved by the injection into the molten copper bath of a reformed gas containing carbon monoxide and hydrogen, see Kuzell et al. U.S. Pat. No. 2,989,397. Such reformed gas is produced in a gas generator by reacting heated air and natural gas in the presence of a catalyst prior to its injection in the bath. However, this requires considerable capital investment in the gasgenerating equipment and entails expenses for its operation and maintenance. Moreover, the time required to effect deoxidation is greater than that required by conventional log polin Objectives: In the making of the present invention, primary objectives were to provide an efficient copper deoxidation process which achieves the desired results in a relatively short operating cycle at relatively low cost, without excessive emission of pollutants to the atmosphere and without the necessity of investing in expensive external equipment.

THE DRAWING Shown in the accompanying drawing is a schematic representation of a refining furnace with preferred procedural steps indicated in the manner of a flow sheet.

SUMMARY OF THE INVENTION According to the invention, a mixture of natural gas and air, or oxygen-enriched air, is introduced into a bath of molten copper containing oxygen. Within the bath, the natural gas is reformed in situ to provide a reducing gas mixture. The oxygen in the air reacts with the hydrocarbon constituents of the natural gas to produce hydrogen, carbon monoxide, and other gaseous reducing agents. The presence of air contained in the natural gas-air mixture also minimizes the production of pollutants from the natural gas. The reducing gas mixture reduces the oxygen contained in the molten copper, forming water vapor. carbon dioxide, and other byproducts.

It is desirable to introduce air over the surface of the copper bath during the injection of the natural gas and air mixture thereinto, so as to generate a reducing atmosphere over the bath by the partial oxidation of the products emanating from the bath. This not only facilitates the reducing operation, but also reduces the quantity of material that would otherwise pollute the atmosphere.

DETAILED DESCRIPTION OF THE BEST MODE PRESENTLY CONTEMPLATED the natural gas, producing hydrogen gas and carbon monox- 0 ide, as well as other products which form a reducing gas mixture. As the reducing gas mixture passes through the bath it reacts with the copper oxides forming water vapor, carbon dioxide, and other products which exit through the surface of the bath. It is possible thereby to reduce the oxygen content of the copper bath to any concentration desired, including the removal of substantially all oxygen within the bath.

Although the composition and concentration of the constituents of natural gas vary somewhat depending upon the source from which the natural gas is obtained, a typical natural gas contains approximately 91 percent methane, approximately 5 percent ethane, and approximately 1.5 percent propane, with trace amounts of other hydrocarbons. In view of the predominance of the lower alkane hydrocarbons in natural gas, gas-air mixtures using gases other than natural gas can be employed in the process. For example, a gas containing principally methane and ethane can be employed, or the individual lower alkane series gases themselves could be used.

The oxygen component of the air in the natural gas-air mixture is the reactive element which combines with the natural gas to form the reducing gas mixture. Pure oxygen or oxygenenriched air can therefore also be employed.

The natural gas-air mixture should contain sufi'icient oxygen to partially oxidize at least enough of the natural gas components to produce a reducing gas mixture within the bath. For purposes of an efficient and rapid reduction of the oxygen present in the copper bath, a natural gas-air mixture containing from approximately 25 percent to 50 percent natural gas is advantageous, although the ratio of natural gas to air can be higher or lower. As the percentage of natural gas in the mixture increases, the concentration of air pollutants emitting from the bath increases. The introduction of air over the bath decreases or eliminates the emission of the pollutants into the atmosphere by reacting with the pollutants to convert them to harmless gaseous products which are not commonly classified as pollutants.

Any means for injecting the mixture into the bath can be used, so long as it introduces the natural gas-air mixture underneath the surface of the copper bath. lt is possible, for example, to use tuyeres, lances, or porous refractories. Excellent results have been obtained in a rotary refining furnace using two or more tuyeres located approximately 18 to 25 inches below the surface of the bath. If a porous refractory is used, care must be taken to prevent the pores of the refractory from becoming clogged when the mixture is not being injected into the bath.

The rate of delivery of the natural gas-air mixture into the bath can be varied and is dependent upon several factors, including the time available for the refining cycle, the quantity of copper in the bath, the concentration of oxygen in the copper, and the number and size of the injection devices used to introduce the mixture into the bath. For example, a large copper charge containing high concentrations of oxygen will require a higher rate of delivery to reduce the oxygen in the same time as will be necessary to reduce a smaller concentration of oxygen in the same quantity of copper. it is desired to inject the mixture into the bath with sufficient velocity to agitate the molten copper. It is advantageous to force the molten copper to erupt into the atmosphere above the surface of the bath. Additional copper is thereby exposed to the reducing atmosphere which has been created above the bath.

Prior processes for reducing the oxygen content of copper have employed a reducing atmosphere above the bath created by introducing a reducing gas over the surface of the bath. According to the process of the invention, however, a nonreduc- In the general test procedure the copper charge was melted and oxidized to a content of from 0.5 to L percent oxygen by injection of air. The copper was then deoxidized by the injection of natural gas or natural gas-air mixtures. The results of these tests are summarized in table I below.

TABLE L-SUMMARY OF DATA FROM SMALL SCALE NATURAL GAS DEOXIDA'IION TESTS Copper analysis, 8.0.!

Natural Natural percent natural gas Copper 1 Reduction Flow rate, s.c.f.m. gas in gas used per lb. charge, Method of time, Mixture, uscd. Initial Final 01 oxygen Test No. pounds injection minutes Gus Air Total percent s.c.f. oxygen oxygen removed 713 P1ug 85 0. 53 0.53 100. 0 45.0 0. 72 0.02 0. 02

593 -d0 90 31 Q0 1. 21 25. 6 28. l K4 02 5. 78

901 Lance. 75 .69 .60 100.0 52.1 .81 .05 7.61

724 do 20 2. 46 2. 46 100. 0 40. .2 73 (H 9. 84

939 do 115 32 85 1.17 27. 4 36 7 .(il .03 6. 40

2 S.c.f. at 14.7 p.s.i.a. and :0

face of the bath. These products include, for example, unreacted hydrocarbons and finely divided carbon. As the products rise from the surface of the bath, they are partially oxidized by the oxygen above the bath, and thereby create a reducing gas mixture. As the molten copper erupts from the surface of the bath, the reducing atmosphere above the bath reacts with the oxygen in the copper, thereby aiding the mixture within the bath in reducing the oxygen content.

An additional important function of the air introduced over the surface of the bath is the conversion of unreacted combustibles into harmless nonpolluting products. This feature of the invention provides a relatively clean process with a considerably lower emission of air pollutants than is encountered with the use of natural gas or other hydrocarbons alone.

Although it is contemplated that the passage of oxygen, air, or oxygen-enriched air over the surface of the bath will be used in conjunction with the feature of the invention relating to the injection of a lower alkane hydrocarbon-oxygen or air mixture into the bath, oxygen, or an oxygen-containing gas such as air, may also be passed over the surface of a bath into which any of the lower alkane hydrocarbons along have been injected, such as propane, butane or natural gas. The passage of such air over the bath creates the reducing gas mixture which aids in reducing the oxygen content ofthe copper, while substantially minimizing the emission of air pollutants, such as finely divided carbon and combustible hydrocarbon normally produced when the lower alkane hydrocarbons are injected along into the bath.

The following examples are intended to illustrate practical applications of the process to the deoxidation of copper. They are not intended to define in any way the scope of the invention. Those skilled in the art will recognize other embodiments ofthe invention which may be applied to particular situations.

EXAMPLE 1 A series of 16 tests was made in which molten copper charges of approximately 800 pounds were treated in a 250 l(.V.A arc furnace. Two types of apparatus were used for gas injection: (1) a submerged lance and (2) a porous plug which was installed in the refractory in the bottom of the furnace lining. The lance construction consisted ofa graphite tube with a 0.25 inch l.D. quartz insert. The porous plug measured 2 inches square II'I cross section and 4 inches in depth, and was of the general type used for inert gas refining in the steel industry.

As noted in the last column, by either injection method, use of the natural gas-air mixture resulted in a lower natural gas requirement per pound of oxygen removed than with the use of natural gas alone. It is also noteworthy that in using natural gas alone a dense carbon soot was produced and emitted from the furnace. Injection of air-natural gas mixtures was very effective in minimizing the emission ofcarbon during the reduction cycle.

EXAMPLE ll On a plant scale basis, a series of deoxidation tests was conducted in which compositions of reducing gas mixtures, and other process variables were investigated. For the initial phase of testing, a rotary refining furnace was equipped with two tuyeres. The tuyeres were installed at a distance of approximately 40 inches on either side of the skimming mouth and at a radial position which would enable a submerged blowing depth of 24 inches. At a later stage of testing. the 2 tuyeres were replaced by 4 tuyeres of similar design. A 1 inch ID 304 stainless steel insert was used in the tuyere assembly and was installed to extend approximately 4 inches beyond the inner surface of the refractory. The test installation included facilities for the delivery, control, and metering of natural gas and air to the furnace. Natural gas and air were obtained from supply lines at nominal pressures of 40 p.s.i.g. and p.s.i.g., respectively.

In the general operating procedure, the copper charge was oxidized and skimmed prior to reduction. Oxidation was accomplished by injecting air through the tuyeres and required from 45 to 90 minutes. Reduction tests were conducted using variable injection rates and various natural gas-air mixtures. In addition, air was passed over the surface ofthe bath.

The test results are shown in table II.

Based on the data shown below. the process provides acceptable results using an average of I75 SCF (Standard Cubic Feet) of natural gas per ton of metal refined of 200 S.C.F. of gas per ton of good anodes cast. The average time required for the reduction ofa charge (250 to 300 tons) varies from approximately L5 to 2.5 hours. The resulting deoxidized copper produces better quality anodes than those produced by conventional poling techniques. Furthermore. as more air is introduced with the natural gas in the mixture, the emission of carbon pollutants IS reduced accordingly.

The temperature of the molten copper bath increases during the period of natural gas-air mixture in ection. This results in a further economy by eliminating the need for normal fuel TABLE IL-SUMMARY OF DATA FROM PLANT SCALE NATURAL GAS DEOXIDATION TESTS Natural Average flow Gas used, Natural Copper refined Reducthrough tnyeres. Natural s.c.f.!ton (opper analysis, percent gas. tion s.c.t.m. 5 gas in V s.c.f./1b. Total Good time, mixture Total Good Initial Final Initial Final oxygen charge anodes min. Gas Air Total percent charge anodes oxygen oxygen sulfur sulfur removed 2 tuyers with 1 inserts 4 tuyets with 1 inserts 240 253 681 934 27. 1 218 26-1 .68 .05 .007 .001 17. 30 188 208 586 884 33. 7 188 210 .00 .07 .010 001 17.77 137 325 599 024 35. 2 162 187 54 .00 011 001 16.88 132 208 424 72? -11. 3 141 161 .52 .07 .007 001 15. 67 90 328 376 704 46. G 120 147 54 11 008 003 1'1. 05 155 28-1 434 718 39. 6 177 203 68 07 026 .001 14. 51 135 315 474 789 39. J 173 221 56 05 015 001 16. 96 200 250 558 808 30. 1) 170 209 G1 O8 023 001 16. 80 115 368 605 973 37.8 171 200 51 .08 .004 001 18. 50 100 376 519 895 42. 0 178 209 .55 10 .006 .002 1!). 78 160 285 700 985 21. 0 162 279 52 06 007 001 17. 61 170 263 688 J51 27. 7 177 206 51 10 .008 00'. 20, 11 Average 261 225 152 304 171 200 17. 22

1 Bath temperatures, without fuel tiring wherein the range of 2,020 to 2,180 F. during the reduction periods.

firing of the furnace during the reduction cycle. As an added feature, substantially all of the residual sulfur contained in the copper from the prior oxidation steps is removed by the process.

We claim:

1. A process for reducing the oxygen content of molten copper, comprising the ste s of:

introducing a mixture 0 at least one lower alkane hydrocarbon and oxygen under the surface ofa bath of molten copper, the quantity of oxygen in said mixture being sufficient to react with at least part of the alkane hydrocarbon to form a reducing gas mixture within the copper bath; and

reducing the oxygen content in the copper bath with said reducing gas mixture.

2. A process as set forth in claim 1, wherein the oxygen in the mixture constitutes a part of a composition selected from the group consisting of air and oxygen-enriched air.

3. A process as set forth in claim 1. wherein the alkane hydrocarbon comprises natural gas.

4. A process as set forth in claim 3, wherein the mixture of natural gas and oxygen contains from 25 to percent natural gas.

5. A process as set forth in claim 1, wherein oxygen is in- 5.0.1.211. 14.7 p.s.i.g.n|n F. (Delivery pressures. alt r the metering station, were in the range 0131 1030 p.s.i.g.i

troduced over the surface of the copper bath to react with combustible materials emanating from the copper bath, said reaction forming a reducing gas mixture above the bath, which removes oxygen from the copper at the liquid-reducing gas interface. and minimizes the emission of air pollutants from the copper bath.

6. A process as set forth in claim 5. wherein the oxygen constitutes a part of a composition selected from the group consisting of air and oxygen-enriched air.

7. In a process for reducing the oxygen content of molten copper wherein at least one lower alkane hydrocarbon is introduced under the surface of a bath of molten copper to reduce the oxygen content of said copper. the improvement comprising introducing oxygen over the surface of the bath to react with combustible materials emanating from the bath, to form a reducing gas mixture over the bath to remove oxygen from the copper at the liquid-reducing gas interface. and to minimize the emission of pollutants to the atmosphere.

8. An improved process as set forth in claim 7, wherein the oxygen introduced over the bath constitutes a part of a composition selected from the group consisting of air and oxygenenriched air. 

2. A process as set forth in claim 1, wherein the oxygen in the mixture constitutes a part of a composition selected from the group consisting of air and oxygen-enriched air.
 3. A process as set forth in claim 1, wherein the alkane hydrocarbon comprises natural gas.
 4. A process as set forth in claim 3, wherein the mixture of natural gas and oxygen contains from 25 to 50 percent natural gas.
 5. A process as set forth in claim 1, wherein oxygen is introduced over the surface of the copper bath to react with combustible materials emanating from the copper bath, said reaction forming a reducing gas mixture above the bath, which removes oxygen from the copper at the liquid-reducing gas interface, and minimizes the emission of air pollutants from the copper bath.
 6. A process as set forth in claim 5, wherein the oxygen constitutes a part of a composition selected from the group consisting of air and oxygen-enriched air.
 7. In a process for reducing the oxygen content of molten copper wherein at least one lower alkane hydrocarbon is introduced under the surface of a bath of molten copper to reduce the oxygen content of said copper, the improvement comprising introducing oxygen over the surface of the bath to react with combustible materials emanating from the bath, to form a reducing gas mixture over the bath to remove oxygen from the copper at the liquid-reducing gas interface, and to minimize the emission of pollutants to the atmosphere.
 8. An improved process as set forth in claim 7, wherein the oxygen introduced over the bath constitutes a part of a composition selected from the group consisting of air and oxygen-enriched air. 